The present invention relates to an angular velocity sensor which can be employed in various control systems, such as a vehicle motion/behavior control system as well as a navigation system, or in a video camera for compensating the operator's hand movements, and more particularly to an angular velocity sensor which detects an angular velocity using a piezoelectric vibrator.
Unexamined Japanese Patent Application No. 7-181042, published in 1995, discloses a conventional angular velocity sensor which comprises a tuning fork vibrator, a drive circuit means for vibrating this vibrator, and an angular velocity sending means for detecting a vibratory movement caused in a direction normal to an oscillating direction of the vibrator, thereby obtaining an angular velocity of the vibrator entered about a predetermined axis.
Furthermore, a diagnosis circuit is provided to detect a failure in the system. A charge amplifier generates an output signal representing a sensed angular velocity. A band pass filter (BPF) is connected to the output terminal of this charge amplifier. A differential amplifier compares the output of the charge amplifier with the output of the BPF. When the obtained differential output is larger than a predetermined reference value, it is judged that the breakdown (such as, exfoliation of a piezoelectric element attached on a piezoelectric body) occurs in the sensor.
However, according to this diagnosis circuit, the differential amplifier produces no differential output signal when a sensing wire is broken, because both the charge amplifier and the BPF produce no output signal (0V). In other words, the diagnosis circuit of this conventional angular velocity sensor cannot detect the breaking of sensor wires.